1. Field of the Invention
The present invention relates to a liquid crystal screen having at least one liquid crystal cell and operating in a reflective mode.
2. Prior Art
Reflective liquid crystal display elements, the optical effect of the represented image can be simply improved by reflecting the oncoming light on a wall component which when considered from the position of the observer, lies at the rear of the screen. Reflectors suitable for this purpose have usually been provided in the form of a vapor-deposited layers of metal on a surface of a rear component or member of the display screen. However, two problems exist with using the metal layer. One of these problems is that the metal layer cannot be in contact with the material of the liquid crystal layer on account of a chemical reaction between the metal layer and the material which reaction would cause damage to the liquid crystal layer. The other problem is providing the layer as close as possible to the liquid crystal layer in order to reduce to a minimum any shading effects or parallax errors which would impair the clarity of the image when it is observed from the other side.
One solution to the above problems is to provide an insulating film which has a thickness of a maximum of 51 .mu.m and which may consist of SiO.sub.2 among other materials. This insulating film acts as electrode bearing transparent layer which is disposed between the liquid crystal layer and the reflective wall component. Such a solution is described in U.S. Pat. No. 3,612,654.
Instead of using an insulating film, it has also been suggested to use a self-supporting thin glass plate having a thickness of preferably 100-300 .mu.m and which is reflective on a rear surface. Such a solution is suggested in a German Offenlegungsschrift 2 338 558.
Both of these screen devices have image representations which, even at large angles of observation, are clear, but nevertheless, these solutions involve a series of fundamental production based shortcomings. For example, as mentioned in the U.S. patent, the insulating film can only be applied in the requisite minimum thickness to the substrate by an expensive process. The thin glass carrier described in the above mentioned Offenlegungsschrift must be provided on one surface with the segmented electrodes and the other surface with the reflecting layer. Then the thin glass carrier is mechanically secured to a thicker glass plate by being pressed thereagainst at increased temperatures and pressures with a thermal plastically deformable synthetic intermediate layer interposed therebetween to hold or secure the two members together.
A liquid crystal display screen, which has a plurality of chambers which are arranged in a series and are separated from one another by glass plates have been suggested. An example is disclosed in U.S. Pat. No. 3,645,604. In these known arrangements, the chambers always form active liquid crystal cells and serve to produce a gray scale.